Flat cables provide a number of advantages wherever there is a need to convey a large number of conductors between electronic equipment and systems. They have a uniform conductor-to-conductor relationship, which makes them easy to use. The physical arrangement of the conductors provides other advantages, such as uniform heat dissipation and compactness.
Structurally, a flat cable is simply a number of insulated conductors or twisted pairs arranged in a parallel, planar configuration and embedded in a layer of plastic. For certain applications, however, such as the interconnection of a disk drive unit and a central processing unit, the flat cable is shielded by enclosing the conductors in a metallic foil layer to provide isolation to external radio frequency or electromagnetic interference. The shielding also prevents RFI/EMI from radiating outward from the cable, an important consideration when having data processing equipment certified under the FCC rules or where data security is important. The metallic foil layer is further surrounded by an insulative jacket, normally of vinyl, which protects the cable from damage and provides strain relief to the internal conductors.
To provide these functions, it is important that the metallic foil layer be grounded to the cabinet of the electronic equipment and that the insulative jacket be fixedly attached to the electronics cabinet to provide strain relief to the cable. Various approaches have been taken to providing a cable clamp or termination assembly that is effective.
U.S. Pat. No. 4,536,053 issued to R. R. Maros, discloses a connector assembly for a shielded, jacketed flat cable, which includes a pair of metallic housing halves to contain the cable. The jacket is stripped back from the end of the cable and the shield is trimmed and folded back on its remaining jacket and positioned in contact with a spring arm or grounding strap mounted in a shallow recess of each housing half. U.S. Pat. No. 4,536,053 also dicusses other termination assemblies for flat cables which may be considered representative.
Another approach to a grounding/strain-relief clamp for flat cables is known, which consists of a pair of spaced, opposing L-shaped grounding plates welded to a flat mounting bracket which, in turn, is bolted to the grounding panel of the electronic device. To use this clamp, the cable jacket is stripped back from the shield, and the shielded cable is passed between the L-shaped plates, through a slot in the bracket, and into an aperture in an grounding panel. A portion of the jacket is positioned between clips on the L-shaped plates, and the plates are bolted together.
This clamp has an important advantage over other types, in that the cable shield is allowed to extend inside the electronics cabinet. In other clamps, the end of the shield remains outside the electronics cabinet or at its entry point, often leaving gaps which partially defeat the function of the foil shield and result in data errors or a compromise of data security. However, this clamp has several disadvantages. Because access to the side of the clamp is required for inserting mounting bolts, an excessive area of the grounding panel is used for each clamp. Furthermore, proper installation of the clamp is somewhat complex, because of the installation of two sets of bolts and jacket retaining clips, and these clamps are often installed incorrectly, again defeating their function.